Arduino + PH probe in Aquarium. Ground Loop. Please help.

Using Arduino Sensors
11

Hi, sorry for the late answer.
It was because in the mean time I contacted Atlas Scientific about this issue. So this was the result:

Ok, this is what to do.
put a NPN mosfet on the ground line going into the E.C. circuit.
You will want to stop all GND from entering the E.C. circuit.
When you take your E.C. reading open the NPN mosfet, take your readings then close the mosfet.
Your pH will still be a little off.
Recalibrate your pH with the E.C. probe in the pH calibration solution (the E.C. probe should be connected to the E.C. circuit and the GND line should be cut off with the PNP mosfet).
This has proven to be successful in fixing the pH / E.C. problem.

Put the NPN Mosfet at the ground line coming into the circuit.
You know, VCC and GND.
Cut the GND line that is powering the circuit not the ground line going to the probe.

As far as which mosfet to buy, there are 100’s.
Here is one that should work well for you: 2N7000_D26Z

Turn on the FET when you take an E.C. reading, turn it off when you are done taking readings.

Yes, place the mosfet between the Arduino and the ground line.

I am not 100% sure the 2N7000 will work .
However, I do believe it will work just fine.
It is a quality FET and that’s generally all you need.

If it were me, I would use it.

So, I'm a little lost where because I didn't understand very well ho to solve this. Anyone help?
In the mean time I bought 2N7000 mosfets:
http://www.fairchildsemi.com/ds/2N/2N7000.pdf

So my understanding I have to put this mosfet between the arduino and the Stamp in the ground line but i don't know how to connect it and use the mosfet.

Thanks for the welp!